Alpha-olefin oligomers and their use as hydraulic fluids and synthetic lubricants (synlubes) are well known. U.S. Pat. No. 2,937,129 reports the oligomerization of C.sub.5-14 .alpha.-olefins using a dialkyl peroxide catalyst to make a synlube. U.S. Pat. No .3,113,167 describes an .alpha.-olefin oligomer process using a titanium halide and an aluminum compound as the oligomerization catalyst.
The preferred catalysts for making .alpha.-olefin oligomers are Friedel Crafts catalysts such as BF.sub.3 as disclosed in U.S. Pat. No. 3,149,178. Optimum properties are obtained starting with 1-decene although mixtures of .alpha.-olefins have been used, cf. U.S. Pat. No. 3,330,883.
The preferred Friedel Crafts catalyst is BF.sub.3. Pure BF.sub.3 is not an effective oligomerization catalyst. A small amount of polar compound is necessary as a promoter. U.S. Pat. No. 3,382,291 describes the use of alcohol promoters such as decanol. Other reported promoters are modenite (hydrogen form), water, phosphoric acid, fatty acids (e.g. valeric acid), ketones, organic esters, ethers, polyhydric alcohols, silica gel and the like.
The most common catalyst, BF.sub.3, can present a disposal problem. Various methods have been devised for removing BF.sub.3 from an oligomerization reaction to achieve an environmentally acceptable result. Vogel et al. U.S. Pat. No. 4,454,366 and U.S. Pat. No. 4,384,162 describe the use of polyvinyl alcohol to remove BF.sub.3 from an oligomerization reaction. Vogel et al. U.S. 4,433,197 contacts the reaction product with silica to remove the BF.sub.3. Morganson et al. U.S. Pat. No. 4,429,177 and Madgavkar et al. U.S. Pat. No. 4,213,001 and U.S. Pat. No. 4,308,414 use silica as an absorbant for BF.sub.3 in an oligomerization process. Madgavkar et al. U.S. Pat. No. 4,394,296 describe the use of wet silica as a co-catalyst with BF.sub.3 in an oligomer process. The silica can be filtered off and recycled as the catalyst. Madgavkar et al. U.S. Pat. No. 4,263,467 remove BF.sub.3 by trickling the reaction product over an inert metallic or ceramic bed whereby the BF.sub.3 is said to evaporate and can be recovered.
From this it can be seen that a great deal of effort has gone into developing a method for removing BF.sub.3 from an olefin oligomerization process in an environmentally safe manner.
Even with these prior methods of trapping BF.sub.3 values, it is not always possible to reduce the boron and fluoride level in the oligomer to an extent such that it can be processed without further clean-up. At some stage an aqueous wash is required. Any water wash will extract boron and fluoride values from the oligomer mixture even if one of the above methods has been used to remove part of the BF.sub.3. Boron and fluoride are considered environmental contaminants and strict limits have been placed in many jurisdiction on the amount of boron and fluoride that can be present in aqueous disposal streams from a chemical plant. The present process provide an environmentally safe method of disposing of aqueous BF.sub.3 solutions without boron or fluoride values escaping into the environment.